1. Field of the Invention
This invention relates to a cutting method and cutting apparatus by which a columnar (cylindrical) or prismatic (e.g. square pillar) base material, such as crystalline ingot, etc., is cut to obtain thin plates, such as wafers, etc., and to be more specific, relates to a cutting method and cutting apparatus by which thin plates, such as wafers, etc., are obtained by a photochemical reaction, etc. that makes use of light energy.
2. Description of the Related Art
Examples of processes, wherein a base material is cut into thin plates, include processes, wherein wafers, to be used for the manufacture of semiconductor devices, are cut from a columnar or prismatic crystalline ingot, comprising a crystal of Si or GaAs, etc.
Among such methods of cutting wafers from an ingot, there are methods of cutting an ingot physically by means of a diamond blade saw or wire saw, etc. However, with such machine cutting methods, a thick cutting margin is necessary and a large amount of the ingot is wasted.
Thus as a method of minimizing the waste of ingot as much as possible, Japanese Laid-Open No. Hei-9-141645 proposes a method, wherein a crystalline ingot is positioned within a chamber into which an etching gas is supplied and the etching gas is excited by illumination of light onto the crystalline ingot, thereby making a component of the etching gas react chemically with the component of the crystalline ingot and volatilizing the component of the crystalline ingot to cut the crystalline ingot and obtain wafers.
The part of the crystalline ingot that is cut is thus gradually removed and formed into a groove by volatilization (etching) from the surface to the interior of the ingot and then becomes completely cut at the final stage.
It is considered that by this cutting method, the cutting margin required for wafer cutting can be made thin in comparison to cases of mechanical cutting.
However, with the cutting method proposed in the abovementioned publication, the illumination of light onto a crystalline ingot is performed through an optical system, comprising a light source and a condenser lens that are disposed at the exterior of the chamber. Though by passage through the condenser lens, a light beam is illuminated in the form of a spot of somewhat restricted range onto the crystalline ingot, since the light beam converges in a cone-like shape up to the illumination spot, as etching progresses, the inner surface of the groove that is formed in the ingot becomes hit with light and the width (thickness) of the groove widens as etching progresses deeper. Thus as is indicated in the abovementioned publication, even if the spot diameter is set to approximately 100 μm, the groove width may greatly exceed several hundred μm. The waste of ingot therefore cannot be made adequately small even when the cutting method proposed in the abovementioned publication is used.
The application of the cutting method proposed in the abovementioned publication to a plurality of parts in the axial direction of the crystalline ingot in order to cut out a plurality of wafers simultaneously may also be considered.
However, if a light source is to be provided for each part that is cut, the arrangement of the cutting apparatus will become complicated and the cost may become high.
The efficiency of processing can be improved by cutting a plurality of wafers or other thin plates simultaneously from a base material, such as a crystalline ingot, etc.
However, if a plurality of wafers or other thin plates are simply cut out simultaneously, these thin plates that have been cut out may collide with each other, thereby leading to flawing of the thin plates.
Though this problem can be resolved by securely supporting the plurality of thin plates that are cut out so that the thin plates will not tilt or become overlapped, this is difficult to achieve in actuality.